This invention relates to compositions of matter comprising novel fractionated agaroid compounds (including agar and agarose), to methods for the preparation of the compositions and to methods for their use.
Agaroid compounds including agar, agarose, derivatized agarose and depolymerized agarose generally are well known in the art.
The closest known prior art to this invention is European Patent Application EP 0 304 024 published Feb. 22, 1989, (corresponding to U.S. Pat. No. 4,990,611 of Feb. 2, 1991) commonly assigned and invented, which discloses the purification of agar or agarose by means of a glycol solution thereof. More specifically, in the disclosed process: (a) agar or agarose is dissolved in a lower alkylene glycol selected from the group consisting of ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, and 1,2-butanediol optionally in the presence of a small amount of water; (b) the solution is heated to a temperature of 50.degree. C. to 130.degree. C.; and (c) upon cooling of the solution to a temperature below 70.degree. C.; (d) a purified agarose (first fraction) precipitates. The precipitate desirably (e) is washed with a volatile organic solvent such as acetone, preferably a lower alkyl alcohol, more preferably methanol, ethanol, or isopropanol, and then dried. The precipitate is disclosed as being extraordinarily soluble in water, in that the water does not need to be heated to dissolve it as in a conventional agarose. There is a disclosure that treatment of the supernatant (still containing a dissolved second agar or agarose fraction) is primarily for the purpose of purifying the glycol for reuse, and that the second agar or agarose fraction present in the supernatant "may either be recovered, as a less pure agarose material, or simply discarded."
The employment of a glycol in conjunction with agar also is taught in U.S. Pat. No. 4,291,025 which discloses a thermally reversible agar gel topical dressing prepared by heating and agitating a mixture of agar, diethylene glycol, and water to solubilize the agar, which is then allowed to cool and form a high strength gel. Formation of a precipitate does not appear to be disclosed. The agar is present in 5-12 wt % and the glycol is not removed but instead comprises from 20 wt % up to a maximum of 75 wt % of the composition. There is a teaching that other polyols such as dipropylene glycol, propylene glycol, or ethylene glycol are not suitable because they do not significantly lower the gelling temperature of aqueous agar gels. Multivalent salts such as sodium borate, potassium borate, potassium sulfate, and zinc sulfate are disclosed as increasing the "toughness" of the gel.
The purification of agarose from crude agar by precipitation from dimethylformamide solvent is disclosed in Chem. Abstracts 74:32889r (1971), which is for Japanese Patent document 45-017,180.
The effect of low molecular weight compounds on the properties of aqueous agarose solutions is discussed in Chem. Abstracts 105:153437j (1986), which states that glycerin and ethylene glycol aid gel formation but that alcohols, dioxane, and urea inhibit gel formation.
U.S. Pat. No. 3,335,127 discloses employing polyethylene glycol to fractionate an agarose product from an agarose/agaropectin mixture, in which the glycol is contacted with an impure agarose aqueous solution at elevated temperatures to precipitate a purified product.